Tracers are referred to as bullets that emit visible light when they are fired from the barrel of a gun. These specialized bullets are created by pressing pyrotechnic material into the small hollow cavity in the back of a bullet. When the bullet is fired, the pyrotechnic material is ignited which causes the bullet to emit light thereby creating a visible aid for the soldier to aim his weapon. Tracers are critical for insuring that successive bullets strike their intended target.
Modern tracers are produced both in the United States and other countries. Most tracer manufacturing facilities are high rate production facilities producing thousand of tracers per hour. To ensure the tracers meet military specifications, representative tracers are taken from the production lot and fired on a test range. At this facility, tracers are tested at night by firing a specified number of rounds and observers score the tracer light intensity by how well they can see it with their unaided eyes. No optics or instrumentation are used in these measurements.
The observers are typically placed at different locations to score by how “well” the tracer rounds perform during flight. For example, if an observer cannot see the tracer it is determined to be a “blind”. If the tracer's light intensity appears to be dim it is determined to be “dim”. At specific distances (depending on the round), the tracer should be at full light intensity. The performance specification for specific rounds (e.g. M62) states how many blinds, muzzle flashes, and dims are allowed for a lot to pass the acceptance test.
One of the biggest drawbacks with this kind of testing is the subjective nature of the tracer evaluation. Human observers evaluate the brightness of the tracer with their eyes. It is well established that different people have different levels of visual acuity. This is due to the makeup of the cones and rods that are part of the eye's retina. Over time the rods and cones undergo changes that affects one's ability to discern an object's brightness. When tracers are tested there is NO quantative data generated other than if the tracer is bright, dim, or blind (not lit or emitting no light). So the manufacturer has no way to quantitatively compare a specific lot of tracers against another lot other than using a subjective system of “blind”, “dim”, or “bright” cateogories. Additionally tracer velocity, another requirement for tracer testing, is measured using a separate system. This adds further time delays and expense to measuring overall tracer performance.
Over the past several years, an alternative system was developed for automating tracer intensity measurements. This system described in “The establishment of threshold criteria for automated acceptance test equipment based on battlefield use of tracer ammunition”, by S. Reilly (26th International Symposium on Ballistics Miami, Fla., Sep. 12-16, 2011), uses Ethernet based video cameras placed at each observer station to capture images of the tracer. By comparing both human observations and the pixel values obtained from the images, the researchers attempted to develop pixel threshold values that could be used to automate the detection of bright, dim, and blind tracers. One of the big issues with this approach is the very small optical cross section of the tracer. A light output tracer only occupies a small number of pixels within the imagers field of view (FOV). Additionally, when tracers are tested on a test range, they are fired from a test weapon at a rate of approximately 1 tracer per second. To keep up with the pace of testing, very rapid pass/fail decisions need to be made to keep up with the test flow. Due to the rapid nature of this testing, camera based systems quantifying pixels taken from an image is not an ideal choice for this kind of measurement due to the large amounts of data generated and the time required to process such data.
Thus, a need exists for a reliable system to quickly, consistently and quantitatively test a tracer's light output. Such system may simultaneously provide velocity data having the added benefit of reducing the time required to test tracers, reduce waste, and provide more substantial information on the tested round.